This invention relates to an adhesion-promoting additive for use in elastomers. In addition, this invention relates to elastomer compositions having enhanced adhesion to other polymers, in particular, to fluoropolymers.
Laminates of elastomers and fluoropolymers are desirable for use in a wide variety of commercial products, for example, in fuel hoses, pump diaphragms, and wire coatings. Good interlayer adhesion is required in such applications in order to produce constructions with acceptable service life. Further, it is desirable that such adhesion be achieved during the laminate curing process, without the necessity of applying primers or adhesives to the uncured elastomer surface.
One method described in the art for promoting interlayer adhesion between dissimilar elastomers and between elastomers and thermoplastic compositions is described in U.S. Pat. No. 5,300,569 and involves addition of polymeric adducts of dicarboxylic acids or dicarboxylic acid derivatives to uncured elastomers to promote adhesion to various substrates. While such systems often provide improvement in adhesion, certain demanding commercial requirements require even greater bond strengths than can be achieved through use of the adducts alone. In addition, the systems disclosed in U.S. Pat. No. 5,300,569 are not suitable for use with certain elastomers, including those mixed with amines or active hydrogen compounds.
The present invention is directed to elastomer compositions which contain polymeric dicarboxylic acids or dicarboxylic acid derivatives, but which exhibit enhanced adhesion to other polymers, especially to fluoropolymers.
In particular, the present invention is directed to a composition for improving adhesion between an elastomer and a fluoropolymer comprising
(A) a first polymer comprising an uncured unsaturated polymeric adduct formed by reacting i) a polymer having unsaturation in the backbone of the polymer chain with ii) an unsaturated dicarboxylic acid or dicarboxylic acid anhydride, wherein the acid or anhydride moieties comprise at least three weight percent of said adduct; and
(B) a compound selected from the group consisting of polyamino primary amines, polyamino primary amine carbamates, and condensation products of polyamino primary amines with aldehydes;
wherein the number of equivalents of component (B) is equal to or greater than the number of equivalents of carboxylic acid moieties or anhydride moieties present in component (A).
The invention is further directed to a composition for improving adhesion between an elastomer and a fluoropolymer comprising
(A) a first polymer comprising an uncured unsaturated polymeric adduct, formed by reacting i) a polymer having unsaturation in the backbone of the polymer chain with ii) an unsaturated dicarboxylic acid or dicarboxylic acid anhydride, wherein the acid or anhydride moieties comprise at least three weight percent of said adduct; and
(B) a polyhydroxy compound; and
(C) a quaternary phosphonium salt vulcanization accelerator or a quaternary ammonium salt vulcanization accelerator;
wherein the number of equivalents of component (B) is equal to or greater than the number of equivalents of carboxylic acid moieties or anhydride moieties present in component (A).
The invention is also directed to a curable elastomer composition which comprises
(A) a first polymer comprising an uncured unsaturated polymeric adduct, formed by reacting i) a polymer having unsaturation in the backbone of the polymer chain with ii) an unsaturated dicarboxylic acid or dicarboxylic acid anhydride, wherein the acid or anhydride moieties comprise at least three weight percent of said adduct;
(B) an elastomer, different from said first polymer;
(C) a compound selected from the group consisting of polyamino primary amines, polyamino primary amine carbamates, and condensation products of polyamino primary amines with aldehydes; and
(D) a curing agent for the elastomer of (B);
wherein the number of equivalents of component (C) is equal to or greater than the number of equivalents of carboxylic acid moieties or anhydride moieties present in component (A).
The invention is additionally directed to a curable elastomer composition which comprises
(A) a first polymer comprising an uncured unsaturated polymeric adduct, formed by reacting i) a polymer having unsaturation in the backbone of the polymer chain with ii) an unsaturated dicarboxylic acid or dicarboxylic acid anhydride, wherein the acid or anhydride moieties comprise at least three weight percent of said adduct;
(B) an elastomer, different from said first polymer;
(C) a polyhydroxy compound;
(D) a quaternary phosphonium salt accelerator or a quaternary ammonium salt vulcanization accelerator; and
(E) a curing agent for the elastomer of (B)
wherein the number of equivalents of component (C) is equal to or greater than the number of equivalents of carboxylic acid moieties or anhydride moieties present in component (A).
The invention is further directed to laminates of the curable elastomeric compositions and fluoropolymer compositions, both fluoroplastics and fluoroelastomers.
Adhesion promoting compositions of the present invention comprise mixtures of carboxylated polymeric adducts and a) polyamines or polyamine derivatives, or b) polyhydroxy compounds. The carboxylated polymeric adducts which are suitable for use in the present invention are disclosed in U.S. Pat. No. 5,300,569. They are prepared by reacting polymeric resins, such as, for example, polybutadiene homopolymers or copolymers of styrene and butadiene, with a dicarboxylic acid or dicarboxylic acid anhydride, such as maleic anhydride. Preferably, the polymeric resin is an unsaturated polymer comprising at least one monomer which is a conjugated diene of 4-12 carbon atoms. The polymer may additionally comprise a monomer which is a vinyl substituted aromatic compound of 8-20 carbon atoms. Polybutadienes are preferred polymers and a preferred polybutadiene is a random 1,2 or 1,4 polybutadiene homopolymer containing 20-90% 1,2 vinyl groups. Polymer molecular weights are generally in the range of 4,000 to 30,000.
The dicarboxylic acid or dicarboxylic acid anhydride which is reacted with the polymeric resin to produce the carboxylated polymeric adducts used in the compositions of the present invention may be any alpha, beta-ethylenically unsaturated dicarboxylic acid or anhydride. Preferably, the adduct is prepared by reaction of maleic acid or maleic anhydride with the polymeric resin. Generally, the unsaturated acid or anhydride comprises at least 3 weight percent of the carboxylated polymer resin adduct, preferably between 3 and 17 weight percent of the polymer resin adduct.
The polyamine compounds and polyamine derivatives suitable for use in the adhesion promoting compositions include primary amines having more than one amino moiety, carbamates having more than one nitrogen-containing moiety derived from polyamino primary amines, and adducts of polyamino primary amines with aldehydes. Examples of suitable polyamino primary amines include ethylenediamine, tetraethylenetetramine, hexamethylenediamine, triethylenetetramine, cumenediamine, tetramethylenediamine, hexamethylenetetramine, 1,2-diaminopropane, diethylaminopropylamine, and 4,4xe2x80x2-methylenebis-(cyclohexylamine). Examples of particularly useful carbamates are hexamethylenediamine carbamate and 4,4xe2x80x2-methylenebis-(cyclohexylamine) carbamate. A preferred polyamino primary amine/aldehyde adduct is N,Nxe2x80x2-di-cinnamylidene-1,6-hexanediamine.
Polyhydroxy compounds may be used in place of the polyamino primary amines or amine derivatives in the compositions of the present invention. Suitable polyhydroxy compounds include bisphenol A, bisphenol AF, bisphenol S, hydroquinone, 4,4xe2x80x2-dihydroxybenzophenone, is catechol, 2,5-dimethyl-hydroquinone, pentaerythritol, 2,2-dimethyl-1,3-propanediol, and trimethylolpropane. Bisphenols are preferred, and, of these, bisphenol AF is most preferred. When a polyhydroxy compound is utilized, an accelerator, such as a tetralkylphosphonium salt or a tetraalkylammonium salt, will be present to achieve optimum adhesion in the cured product. Such accelerators are disclosed in Schmiegel, U.S. Pat. No. 4,496,682; in Kometani et al., U.S. Pat. No. 3,864,298; and in Patel, U.S. Pat. No. 3,655,727. Preferred accelerators are benzyltriphenylphosphonium chloride, benzyltriphenylphosphonium bromide, benzyltriphenyl-phosphonium phenolate of bisphenol AF, tetrabutylammonium hydrogen sulfate, and tetrabutylammonium bromide.
The amount of polyamino compound, polyamino compound derivative, or polyhydroxy compound which is mixed with the carboxylic acid or anhydride adduct is adjusted so that it is equal to or greater than the amount necessary to completely react with the free carboxylic acid or carboxylic anhydride moieties of the polymeric adduct component of the composition. That is, the number of equivalents of free amino moieties, blocked amino moieties, or free hydroxyl moieties present must be equal to or greater than the number of equivalents of carboxylic acid or carboxylic acid anhydride present in the polymeric adduct. Generally, about 1.25-2.0 equivalents of polyamino compound, polyamino compound derivative, or polyhydroxy compound per equivalent of carboxylic acid or anhydride moiety are sufficient. The adhesion promoter is conveniently prepared by physically mixing the components. When used on a commercial scale, it is most convenient to mill or mix the components of the adhesion promoting composition directly into an elastomer composition without the ingredients of the adhesion promoting composition being subjected to a prior mixing step.
A further embodiment of the present invention comprises curable elastomer compositions which exhibit excellent adhesion to fluoropolymer substrates. A first type of curable composition comprises four principal components: a) an adduct of an unsaturated polymer and dicarboxylic acid or dicarboxylic acid anhydride; b) an elastomer, different from the polymeric component of a); c) a polyamine or polyamino compound derivative; and d) a curing agent for the component b) elastomer. A second type of curable composition comprises five principal components: a) an adduct of an unsaturated polymer and dicarboxylic acid or dicarboxylic acid anhydride; b) an elastomer, different from the polymeric component of a); c) a polyhydroxy compound; d) an accelerator; and e) a curing agent for the elastomer of component b).
The first component of the curable compositions is a member of the class of dicarboxylic acid or dicarboxylic acid anhydride polymeric adducts described above and disclosed in U.S. Pat. No. 5,300,569.
The elastomer which is the second component of the curable composition is an elastomeric polymer which will co-cure with the polymeric adduct. Examples of such elastomers include chlorinated olefin polymers, such as chlorinated polyethylene; acrylonitrile butadiene rubber; polychloroprene homopolymers and copolymers; ethylene propylene copolymer rubber and EPDM copolymer rubbers; chlorosulfonated olefin polymers, such as chlorosulfonated polyethylene and chlorosulfonated ethylene alpha-olefin copolymers; elastomeric copolymers of ethylene and polar comonomers, such as ethylene acrylic elastomers; polysiloxanes, including fluorinated polysiloxanes; fluoroelastomers; epichlorohydrin rubber; polyacrylates; butyl rubber; and halobutyl rubber. Preferred elastomers are elastomeric ethylene copolymers with polar comonomers.
The preferred ethylene copolymer elastomers are elastomeric copolymers of ethylene and at least one other polar monomer. Such monomers include (a) C1-C8 alkyl esters of acrylic or methacrylic acid or (b) vinyl esters of C2-C8 carboxylic acids. The ethylene content of these copolymers is about 20-55 wt. %, preferably 20-45 wt. %. The alkyl (meth)acrylate or the vinyl ester comonomers comprise about 45-80 wt. % of the polymer, preferably about 55-80 wt. %. Alkyl acrylates and alkyl methacrylates suitable for use in the polymers include C1-C8 alkyl esters of acrylic acid or methacrylic acid, for example, the methyl, ethyl, isobutyl, hexyl, and 2-ethylhexyl esters. Methyl, ethyl, and butyl acrylates are preferred. Methyl acrylate is most preferred. Vinyl esters of carboxylic acids suitable for use in the polymers include vinyl esters of carboxylic acids having 2-8 carbon atoms, for example, vinyl acetate, vinyl propionate, vinyl hexanoate, and vinyl 2-ethylhexanoate. Vinyl acetate is preferred. The Mooney viscosity of elastomeric ethylene copolymers which can be used in the present invention is generally 10-120, preferably 10-50 (ASTM D-1646, 100xc2x0 C., 1 minute preheat, viscosity measured at 4 minutes).
Ethylene copolymers of this type are generally prepared by continuous copolymerization of ethylene and comonomers in a stirred reactor in the presence of at least one free radical initiator at temperatures of from 120xc2x0 C. to 300xc2x0 C. and at pressures of from 130 to 310 MPa. Optionally, lo the copolymers are prepared in the presence of about 2-25 wt. % methanol or acetone so that reactor fouling is decreased or eliminated, as disclosed in U.S. Pat. No. 5,028,674.
Representative examples of specific ethylene copolymers include ethylene/methyl acrylate, ethylene/methyl methacrylate, ethylene/ethyl acrylate, ethylene/ethyl methacrylate, ethylene/butyl acrylate, and ethylene/2-ethylhexyl methacrylate. Further representative examples include ethylene/methyl acrylate/carbon monoxide, ethylene/butyl acrylate/carbon monoxide, and ethylene/vinyl acetate/carbon monoxide.
The polyamino compounds, polyamino compound derivatives, or polyhydroxy compounds useful as the third component of the curable compositions of the invention are the polyamino compounds, polyamino compound derivatives, and polyhydroxy compounds described above as components of the adhesion promoting compositions of the present invention. Likewise, it is necessary that these compounds are present in an amount sufficient to react with substantially all the free carboxylic and anhydride moieties present in the dicarboxylic acid or dicarboxylic acid anhydride polymeric adduct. Consequently, the number of equivalents of amino or hydroxy moieties present must be equal to or greater than the number of equivalents of carboxylic acid or carboxylic acid anhydride present in the polymeric adduct. As in the adhesion promoting composition, generally about 1.25-2.0 equivalents of polyamino compound, polyamino compound derivative, or polyhydroxy compound is used per equivalent of dicarboxylic acid or anhydride adduct. When a polyhydroxy compound is utilized, an accelerator which is a tetralkyl phosphonium salt or tetraalkylammonium salt is present in order to achieve optimum adhesive properties.
The elastomer component of the curable composition is the major ingredient of the curable compositions of the present invention. Generally, the dicarboxylic acid or dicarboxylic acid anhydride polymeric adduct will be present in amounts of 2-20 parts by weight per 100 parts of the elastomer, preferably in amounts of4-10 parts per 100 parts of the is elastomer.
The curable elastomeric blends are crosslinked with a vulcanizing agent suitable for the particular elastomeric component of the composition.
For example, in the case of the preferred ethylene copolymers, a peroxide curing agent is generally used. The curing agent is preferably a composition which generates free radicals at curing temperatures. A dialkyl peroxide which decomposes at a temperature above 50xc2x0 C. is especially preferred. Among the most useful peroxides are 2,5-dimethyl-2,5-di(tertiary butylperoxy)hexyne and 2,5-dimethyl-2,5-di(tertiarybutyl-peroxy)hexane, dicumyl peroxide, dibenzoyl peroxide, tertiarybutyl perbenzoate, and di[1,3-dimethyl-3-t-butylperoxy)butyl]carbonate. Other curing agents may also be used. For example, a sulfur curative is usually the curative of choice for EPDM copolymers. The appropriate amount of curative employed with a particular elastomer will be that conventionally used in the art. In the case of peroxide curatives, this is usually about 2-7 parts per 100 parts rubber. In general, the dicarboxylic acid or dicarboxylic acid anhydride adduct; non-fluorinated elastomer; polyamino compound, polyamino compound derivative, or polyhydroxy compound/accelerator; and curing agent will be blended on a rubber mill or in an internal mixer, for example, a Banbury mixer, at a temperature below that necessary to initiate cure. In addition to curing agent, various other additives which are conventional elastomer compounding ingredients may be added to the curable composition. These include metal oxides and hydroxides; fillers, such as carbon black, clay, silica, non-fibrillating fluoropolymers, and talc; pigments; antioxidants; antiozonants; plasticizers; accelerators; curative coagents; stabilizers; and waxes. Usually, amounts of from 5-75 parts of a given additive per hundred parts of the elastomeric polymer is used. The is specific amounts will depend on the particular application and physical properties which are to be optimized.
A further embodiment of the present invention comprises a laminate of the curable composition of the present invention with a fluoropolymer, preferably a fluoroplastic which has been treated to promote adhesion. This is of particular utility in applications wherein a laminate having low fuel permeability under high temperature conditions is desired. For example, in U.S. Pat. No. 5,427,831 fuel resistant laminates are disclosed having an elastomeric layer, a non-elastomeric fluoropolymer layer which has been treated to promote adhesion, and an elastomeric covering layer. It is often difficult to adhere the covering layer to the treated fluoropolymer layer, despite adhesion promoting treatment of the fluoropolymer surface, i.e. generally plasma treatment, corona discharge treatment, or sodium etching. It has been found that the curable compositions of the present invention, when laminated to the treated fluoropolymer, exhibit enhanced adhesion, particularly when elastomeric ethylene copolymers with polar comonomers are utilized as the elastomer component. The non-elastomeric fluoropolymer layer is preferably composed of non-elastomeric tetrafluoroethylene polymers, including polytetrafluoroethylene, copolymers of tetrafluoroethylene and hexafluoropropylene, copolymers of tetrafluoroethylene and perfluoro(alkyl vinyl) ether and copolymers of tetrafluoroethylene and ethylene. Copolymers of ethylene and chlorotrifluoroethylene may also be employed. Polyvinylidene fluoride or copolymers of vinylidene fluoride with at least one monomer selected from the group consisting of hexafluoropropylene and tetrafluoroethylene are less preferred, but may be utilized. Lamination of the elastomeric and fluoropolymer layers and cure of the elastomeric layers generally takes place in a single operation, for example, by heating the laminate, optionally under pressure, at temperatures of from 140xc2x0 C.-200xc2x0 C.
Although lamination to treated fluoroplastics is a preferred embodiment of the present invention, lamination of the curable elastomer composition to fluoroelastomer compositions, including perfluoroelastomer compositions, is also contemplated.
The adhesion promoting compositions of the present invention are particularly useful in promoting adhesion between non-polar elastomers and fluoropolymers, especially in applications wherein laminates are required which are exposed to high temperatures. In particular, they are useful components in compositions employed in fuel hose laminates and wire covering.
In one particularly preferred embodiment, a laminar structure is formed having at least three layers. The first layer, having a thickness of 0.1 to 4 mm comprises i) an unsaturated polymeric adduct formed by reacting a polymer having unsaturation in the backbone of the polymer chain with an unsaturated dicarboxylic acid or dicarboxylic acid anhydride, wherein the acid or anhydride moieties comprise at least three weight percent of said adduct; (ii) an elastomer, different from the unsaturated polymer of (i); (iii) a compound selected from the group consisting of polyamino primary amines and derivatives of the polyaminoprimary amines; and (iv) a curing agent for the elastomer of (ii). The number of equivalents of component (iii) is equal to or greater than the number of equivalents of carboxylic acid moieties or anhydride moieties present in component (i). The second layer, which is in contact with the first layer, has a thickness of 0.01 to 0.1 mm and comprises a non-elastomeric fluoropolymer which has been treated to promote adhesion by corona discharge, sodium etching, or plasma treatment. The third layer, in contact with the second layer, has a thickness of 0.1 to 1.5 mm and comprises an elastomer, which may be either the same as the elastomer of the first layer or a second elastomer. Preferably, the third layer is a fluoroelastomer.
The elastomer of the first and third layers may be selected from a large variety of elastomer types, including acrylonitrile butadiene rubbers, copolymers of epichlorohydrin and ethylene oxide, hydrogenated acrylonitirile butadiene rubbers, and fluoroelastomers. The structure may further comprise a reinforcing braiding, preferably of a polyester or a polyaramid. The structure may be in the form of a hose or a tube.
In another preferred embodiment, the first layer contains a combination of a polyhydroxy compound and a tetraalkylphosphonium salt vulcanization accelerator or a tetraalkylammonium salt vulcanization accelerator in place of the polyamine, for purposes of promoting adhesion between the first and second layers.
The adhesion promoting compositions of the present invention are particularly suited for use in enhancing adhesion of non-fluorinated elastomers to fluoroplastics, and are especially useful in production of laminated fuel hoses. However, they would also be useful in enhancing adhesion of non-fluorinated elastomer to treated fluoroplastics in the manufacture of food conveyer belting, pumps, and diaphragms.